An optical switch is a device where information-bearing light may be directed to one of several outputs. Prior art optical switches have, mainly, been integrated optical waveguide structures such as titanium-diffused (Ti) waveguides in lithium-niobate (LiNbO3) or gallium-arsenide (GaAs) structures or other compound semiconductors. One problem with integrated optic switches is that they may be connected to an optic fiber since such fibers are the primary carriers of optical communications. Coupling between integrated optic switches and optical fiber is an inefficient process because of the modal fields of these two elements are not compatible, and large differences in the indices of refraction lead to large reflection losses.
The prior art optical switches have been controlled, primarily, by electro-optic or acousto-optic techniques. In such an arrangement, the waveguides of the optical switch are separated or surrounded by electro-optic, or acousto-optic, material that controls the coupling between the waveguides. Such control is not the fastest control possible because coupling in such devices occurs through the electro-optic, or acousto-optic, material. Also, Such control does not provide a system optimized with respect to the number of elements contained therein.
An optical switch comprising two optical fibers has been suggested where switching is controlled by varying the index of refraction of one of the fibers. One of the fibers must exhibit a large non-linear optical coefficient and a linear index of refraction. Since fiber optic transmission lines do not, typically, exhibit both of these characteristics, losses may occur where such a switch is coupled to the fiber optic transmission lines due to the mismatch of materials. Furthermore, there is no isolation between the control signal and the optical signal in such a device, and undesirable interaction may occur.
In an article entitled "Investigation of Coupling Between a Fiber and an Infinite Slab," published by the IEEE in The Journal of Lightwave Technology, Vol. 7, No. 1, January 1989, Dietrich Marcuse discloses a two-fiber optical switch as described above where one of the fibers is replaced with a slab waveguide. Although the slab waveguide provides benefits such as providing couplings between more modes than can a two-fiber optical switch, a slab-fiber optical switch still suffers from the problems listed above for a two-fiber optical switch.
U.S. Pat. No. 3,208,342, entitled "ELECTRO-OPTIC LIGHT COUPLING OF OPTICAL FIBERS"; U.S. Pat. No. 4,012,113, entitled "ADJUSTABLE OPTICAL SWITCH OR MODULATOR"; U.S. Pat. No. 4,035,058, entitled "ELECTRO-OPTICAL SWITCH AND A METHOD OF MANUFACTURING SAME"; U.S. Pat. No. 4,842,368, entitled "NXN SINGLE-MODE OPTICAL WAVEGUIDE COUPLER"; and U.S. Pat. No. 4,991,920, entitled "OPTICAL CONVERTER"; each disclose a device for coupling light. These devices each suffer from the problems listed above for an electro-optic device. U.S. Pat. Nos. 3,208,342; 4,012,113; 4,035,058; 4,842,368; and 4,991,920 are hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 3,899,235, entitled "SLAB-COUPLED OPTICAL WAVEGUIDE," discloses a device for coupling light. Such a device suffers from the problems listed above for a two-fiber optical switch where one of the fibers is replaced with a slab waveguide. U.S. Pat. No. 3,899,235 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,491,763, entitled "OPTICAL HYBRID WITH 3.times.3 COUPLING DEVICE," discloses a device for coupling light. Such a device includes a first waveguide and a second waveguide of identical index of refraction placed symmetrically about a third waveguide of a different and fixed index of refraction so that the first waveguide and the second waveguide have the same optical coupling to the third waveguide. The device of U.S. Pat. No. 5,491,763 is not maximally efficient since the light coupled between the first waveguide and the second waveguide must pass through the third waveguide. Also, the index of refraction of the third waveguide is fixed so that light is always coupled between the first waveguide and the second waveguide. U.S. Pat. No. 5,491,763 is hereby incorporated by reference into the specification of the present invention.